High Performance Fibers (HPFs) are being proposed for expanding uses in many specialized applications, such as military and aerospace (turbo machinery, rockets, advanced structures), automobile, biomedical, energy, and other applications that require advanced materials with exceptional strength, stiffness, heat resistance, and/or chemical resistance. HPFs are sought when a combination of extreme material properties is required which cannot be met by existing metal filaments or by carbon, glass, vegetal or mineral fibers. HPF composite systems generally include a plurality of coated fibers, distributed within a “matrix.”
Almost all inorganic (ceramic) fibers are produced today by forcing a liquid polymeric precursor (such as polycarbosilanes for silicon carbide [SiC] fibers) that carries the elements of interest through a spinneret to produce what are called green fibers, which are then heated in kilns or furnaces to pyrolyze and sinter the materials into an acceptable fiber. One consequence of this approach has been that unwanted impurities—in particular oxygen—are typically left behind and “locked in” to the final product. In SiC fibers, for example, this gives rise to oxy-carbide impurity phases in the fiber microstructure which tends to decompose into gases at high temperature, thus limiting the temperatures at which such fibers can be used.